Structural Origin of Thermally Induced Second Harmonic Generation Enhancement in RbNaMgP₂O₇

Abstract

RbNaMgP 2 O 7 is a newly reported nonlinear optical (NLO) crystal that displays remarkable second harmonic generation (SHG) enhancement upon heating. In this work, we carried out in situ neutron powder diffraction and impedance spectroscopy measurements through its polar-to-polar phase-transition region and confirmed that the dynamic process for the alignment of NLO-active anionic [P 2 O 7 ] 4− groups is composed of thermoinduced incremental rotation of [P 2 O 7 ] 4− groups, which is accompanied by cationic migration enhancement. Furthermore, we elucidated a new mechanism of coupling between anionic group alignment and cationic migration for the first time in NLO materials. This mechanism could offer extra freedom for new NLO material design and anionic group alignment control for a better SHG response via tuning the cationic migration.

Two Pyrophosphates with Large Birefringences and Second‐Harmonic Responses as Ultraviolet Nonlinear Optical Materials

“…As we know that due to the rigid structure of PO 4 tetrahedron, many phosphates own relative small birefringences,s uch as Ba 2 NaClP 2 O 7 (0.017 at 1064 nm), [17] KLa(PO 4 ) 3 (0.008 at 1064 nm), [15] CsLa(PO 4 ) 3 (0.0068 at 1064 nm) [16] and so on (shown in Table 1). The birefringence of the I is comparable to RbNaMgP 2 O 7 (0.035 (HTP) and 0.031 (LTP) at 532 nm, respectively), [25] Ba 3 P 3 O 10 Br (0.023 at 1064 nm and 0.024 at 532 nm) [12] and Ba 3 P 3 O 10 Cl (0.028 at 1064 nm and 0.030 at 532 nm). [12] As described above,f rom the states among the Fermi level, we can deduce that the P-O,Pb-O,and Bi-O polyhedra would give main contribution to the optical properties of I (RbPbBi531).…”

“…TheS HG intensities increase with increasing particle sizes until particle sizes are independent and so both compounds are type IPMa ccording to the rule proposed by Kurtz and Perry. [22] Noteworthy, I is the largest known to date in PM UV NLO pyrophosphates,s uch as CsLiCdP 2 O 7 (1.5 KDP), [23] K 4 Mg 4 (P 2 O 7 ) 3 (1.3 KDP), [13] Rb 4 Mg 4 (P 2 O 7 ) 3 (1.4 KDP), [13] Ba 2 NaClP 2 O 7 (0.9 KDP), [17] as well as CsNaMg-P 2 O 7 (1.1 KDP) [24] and RbNaMgP 2 O 7 (HTP) (1.4 KDP) [25] ( Table 1).…”

Optical Interpretation of a Second-Order Phase Transition Induced by Thermal-Driven Li+ Migration via Configurational Entropy in CaTiO3:Li+,Yb3+,Er3+

“…These processes and property variations might be accompanied by a phase transition. However, the study of the thermodynamics and microstructure variation of the processes in an optical view is scarce in optical materials, even though it is common in the ion-conductive materials. − …”

Designing a Deep-UV Nonlinear Optical Fluorooxosilicophosphate

“…In 2014, Chen and coauthors discovered the first deep-UV NLO phosphate, Ba 3 P 3 O 10 X (X = Cl, Br), prompting scientists to consider that non-π-conjugated systems may be good candidates for deep-UV NLO materials. Since then, a variety of phosphates with excellent deep-UV NLO properties have been synthesized, such as Ba 5 P 6 O 20 , Cs 2 LiPO 4 , RbNaMgP 2 O 7 , Ba 2 NaClP 2 O 7 , and monofluorophosphates such as (NH 4 ) 2 PO 3 F and NaNH 4 PO 3 F . Recently, our group synthesized two new sulfates, (NH 4 ) 2 Na 3 Li 9 (SO 4 ) 7 and NH 4 NaLi 2 (SO 4 ) 2 , which show attractive prospects as non-π-conjugated deep-UV NLO materials.…”